One of the most visible signs of aging in humans is the changes experienced by the skin: dryness, appearance of spots, flaccidity and wrinkles. These effects can be caused by external agents such as the constant exposure to the sun, atmospheric pollution or the contact with chemical agents present in, for example, cleansing products, but they are also a consequence of intrinsic physiological, biochemical and histological changes in the human organism, due to the decrease in the synthesis of proteins such as collagen or elastin, to an increase in proteolysis, and to a general breaking of the skin barrier, of the connective tissue and of cohesion.
Different active ingredients have been described for preventing and decreasing aging symptoms, such as for example, retinoids, hydroxy acids, flavonoids or derivatives of vitamin C and E. Said compounds normally act by improving skin hydration, increasing cell renovation or preventing the degeneration of the tissues forming the skin; however, their efficacy in preventing or treating facial wrinkles caused by muscle contraction is limited. There is therefore a need to develop new active ingredients with proven efficacy for the preparation of a cosmetic or dermopharmaceutical composition to reduce and/or eliminate facial wrinkles, especially expression wrinkles.
Expression wrinkles are considered to be those which are a result of the stress exerted by the contractions of the facial muscles responsible for producing facial expressions on the skin of the face. Expression wrinkles are usually located on the forehead, in the space between the eyebrows, around the mouth and/or around the eyes. Depending on the shape of the face, the frequency of the expressions and the existence of tics (convulsive movements which are frequently repeated and are caused by the involuntary contraction of one or several muscles, in this case, of the face), expression wrinkles can even appear in adolescence. External factors such as exposure to sun can emphasize their depth and visibility.
Botulinum toxins have been widely used with the aim of reducing and/or eliminating expression wrinkles, especially serotype A (BOTOX® Cosmetic, Allergan) [Carruthers J. D. and Carruthers J. A. (1992) Treatment of glabellar frown lines with C. botulinum-A exotoxin, J. Dermatol. Surg. Oncol. 18, 17-21; Mendez-Eastman S. K. (2003) BOTOX: a review, Plast. Surg. Nurs. 23, 64-69]. However, botulinum toxins have important drawbacks such as the requirement of their application by a doctor by means of an injection, as well as the occurrence of an immune response involving a decrease in the efficacy of the treatment over time.
The cosmetic industry has carried out important efforts to develop compounds imitating the action of botulinum toxins in the treatment and prevention of expression wrinkles. Patent application EP 1,180,524 of Lipotec, S. A. describes peptides derived from the N-terminal fragment of protein SNAP-25 having an anti-wrinkle effect, because they act with a mechanism similar to that of the botulinum toxin: the inhibition of the SNARE complex, a neuronal exocytosis mediator, involves the decrease in the release of neurotransmitters. International application WO97/34620 also describes peptides derived from the amino acid sequence of protein SNAP-25, specifically from the C-terminal region, which can inhibit neuronal exocytosis. The topical application of said compounds is becoming a possible solution for the reduction and/or elimination of expression wrinkles.
Other methods described for the reduction and/or elimination of expression wrinkles involves the use of calcium channel antagonists, particularly salts of manganese (FR 2,809,005) or alverine (FR2,798,590), chloride channel agonists such as glycine (EP 0,704,210) or Iris pallida extracts (FR 2,746,641), certain secondary or tertiary amines (FR 2,845,288 and FR 2,847,250), sapogenins (FR 2,838,344), limonoid compounds (US 2004/127,556) or boswellic acids (FR 2,850,573).
The applicant of the present invention has determined that the peptides derived from the enkephalin sequence are effective in the reduction and/or elimination of facial wrinkles, especially expression wrinkles, acting by means of mechanisms different from those known in the state of the art.
Up until now, the cosmetic or dermopharmaceutical application of enkephalins has been limited to: patent application FR 2,735,687 describes the topical use of enkephalins and their derivatives as compounds with slimming capacity due to their lypolytic activity, whereas patent application FR 2,857,588 describes the topical use of sequences derived from endorphin, including several enkephalin derivatives, to improve the skin barrier function, as well as to improve skin hydration and luminosity or to prevent the effect of atmospheric pollution on the skin.
None of the patents described previously relates to the use of enkephalins as anti-wrinkle agents, or specifically to the use of enkephalin-derived peptides for the reduction and/or elimination of expression wrinkles.
Enkephalins are a family of peptides derived from β-endorphins which can inhibit neuronal activity [Kieffer, B. L. and Gavériaux-Ruff, C. (2002) Exploring the opioid system by gene knockout (2002) Prog. Neurobiol. 66, 285-306]. The specific interaction of these peptides with their neuronal receptors causes a metabolic change in the neurons, which causes a decrease in neuronal activity. Although the action mechanism is currently being investigated, it is known that enkephalins can indirectly modulate the activity of voltage-dependent ion channels, especially the selective K+ channel. [Faber, E. S. and Sah, P. (2004) Opioids inhibit lateral amygdala pyramidal neurons by enhancing a dendritic potassium current. J. Neurosci. 24, 3031-3039]. From the point of view of action mechanism, the binding of the enkephalin to its active receptor activates a trimeric G protein complex, causing the release of Ca2+ from intracellular reserves through the inositol phosphate receptor. Cytosolic calcium acts as an intracellular messenger triggering the activation of signaling pathways involving kinase and phosphatase proteins which chemically modify cellular proteins including ion channels. The modification of ion channels modifies their function; for example, enkephalins activate K+ currents in neurons causing a hyperpolarizing effect. The result of this hyperpolarization is a reduction in Ca2+ cation-dependent neuronal exocytosis, which in turn, decreases the communication in neuronal synapses.
The overall end result is a reduction in the excitability of neuronal synapses as a result of lower neurotransmitter release [Bergevin, A., Girardot, D., Bourque, M. J. and Trudeau, L. E. (2002) Presynaptic mu-opioid receptors regulate a late step of the secretory process in rat ventral tegmental area GABAergic neurons. Neuropharmacology, 42, 1065-1078]. Therefore, an action of enkephalins is neurosecretion inhibition by a mechanism which is different from that described for botulinum toxin and peptides imitating the action of the latter. As a result, and like botulinum toxin and neuronal exocytosis inhibiting peptides, enkephalins also block Ca2+ cation-dependent neuronal exocytosis.
Patent application FR 2,846,885 describes the synergistic effect of the combination of neuronal exocytosis inhibiting peptides, such as those described in patent applications EP 1,180,524 and WO97/34620, together with calcium channel inhibitors. Said invention is restricted to calcium channel inhibitors acting at the membrane level by inhibiting the entrance of calcium, or to compounds acting from inside the neurons, either releasing the intracellular reserves of calcium, or inhibiting the formation of the calcium-calmodulin complex. A person skilled in the art could not deduce the existence of a synergism in the anti-wrinkle effect when neuronal exocytosis inhibiting peptides derived from the SNAP-25 sequence and enkephalins are combined, because the latter act indirectly on potassium channels and not on sodium channels.